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Related Topic: Organic Chemistry 1

Related Subtopic: Chemical properties of alkenes



Questions 3.2.5

Based on the demonstrations,

  1. What is the effect, if any, of ethene on a glowing splint and wet litmus paper?
  2. Describe what is observed when ethene is bubbled through chlorine water, and write an equation for the reaction.
  3. Ethene undergoes addition reaction with chlorine gas (and other halogens) even in the dark. Describe the observations made, and write an equation for the reaction.
  4. How can we use reaction with chlorine to distinguish ethene from ethane?
  5. Describe the effect of ethene on acidified (a) potassium manganate (VII) and (b) potassium chromate (VI).
  6. From the product, how can we know whether an alkene was reacted with chlorine water or chlorine gas?

    7. Other reactions of ethene (and other alkenes)


  7. Ethene undergoes addition reactions with hydrogen halides (HCl, HBr, HI) to form alkyl halides. Write equations for the reaction with each hydrogen halide.
  8. As a hydrocarbon, ethene burns in the same manner as alkanes. Write an equation for the burning of ethene in oxygen.
  9. Ethene undergoes addition reaction with hydrogen gas (hydrogenation) to form ethane. A temperature of 140 oC and nickel catalyst are required. Write an equation for the reaction.
  10. Complete the statement, "Alkenes undergo addition reactions but alkanes undergo - - - reactions".
  11. Many (10 000 and more) molecules of the same ethene can combine with one another in a process called addition polymerization. The product is polythene.
    Write an equation for the reaction.
  12. Alkenes react with concentrated sulphuric acid to form alkylhydrogensulphates. The ions H+ and HSO4- from the acid add to the double bond. Write the formula of the product.



Answers to Questions 3.2.5


  1. Ethene extinguishes a glowing splint and has no observable effect on wet litmus.
  2. Ethene turns chlorine water colourless (decolourizes chlorine water).
    CH2CH2(g) + HOCl(aq) → CH2ClCH2OH(l)

  3. Colour (of chlorine gas) changes from pale green to colourless.
    CH2CH2(g) + Cl2(g) → CH2ClCH2Cl(l) (1,1-dichloroethane)

  4. Reaction (and decolourization) with ethene occurs even in the dark; but reaction with ethane (an alkane) requires presence of light (ultraviolet light).
  5. Ethene decouries acidified potassium manganate (VII) solution. It turns potassium chromate (VI) from orange to green).
  6. With chlorine gas, the product is dichloroethane; but with chlorine water, the product has an -OH group on one carbon atom.
  7. CH2CH2 + HCl(g) → CH3CH2Cl CH2CH2 + HBr(g) → CH3CH2Br
    CH2CH2 + HI(g) → CH3CH2I

  8. CH2CH2(g) + 3O2(g) → 2H2O(g) + 2CO2(g)
  9. CH2CH2(g) + H2(g) → CH3CH3(g) (in presence of nickel catalyst at 140 oC)
  10. "Alkenes undergo addition reactions but alkanes undergo substitution reactions".
  11. nCH2CH2 → (-CH2CH2-)n
  12. CH3CH2HSO4